Hydrocarbon synthesis from synthesis gas (syngas) containing hydrogen and carbon monoxide in the presence of a Fischer-Tropsch (FT) synthesis catalyst is commonly known as FT synthesis. During the FT synthesis, the syngas is contacted with the FT synthesis catalyst under FT synthesis conditions to produce the hydrocarbons. One type of catalyst which is often used in low temperature FT (LTFT) synthesis comprises an active catalyst component such as Co supported on and/or in a catalyst support such as alumina, silica, titania, magnesia or the like, and the hydrocarbons produced are usually in the form of a waxy hydrocarbon product.
It is known that during FT synthesis the activity of catalysts, such as Co supported on a support usually decreases over time (that is, the catalyst deactivates), with the result that less syngas is converted into hydrocarbons. This characteristic of a catalyst that its activity may decrease over time during hydrocarbon synthesis is referred to as the activity stability of the catalyst.
As stated above, a lack of activity stability of a catalyst has the effect that the catalyst deactivates over time and less hydrocarbons are then produced. To counter this effect, the temperature of the FT synthesis process may be increased to make up for the loss of activity of the catalyst. However, an increased reaction temperature has the disadvantage that more unwanted methane is formed during the FT synthesis. Other costly measurements such as increased catalyst loading, catalyst rejuvenation or catalyst reactivation may also be taken to recover the hydrocarbon production.
It is known in the art that many different components such as modifiers, dopants and promoters may be introduced into catalysts in order to improve certain aspects of the catalyst, such as improved hydrothermal stability, improved reducibility of the active component, improved activity of the catalyst, improved product selectivity of the catalyst and improved activity stability of the catalyst during FT synthesis. A long list of such components is known to be suitable for the purposes set out above, for example Si, Ti, Zr, Cu, Zn, Ba, Co, Ni, La, W, Na, K, Ca, Sn, Cr, Fe, Li, Tl, Mg, Sr, Ga, Sb, V, Hf, Th, Ce, Ge, U, Nb, Ta, Mn, Pt, Pd, Re and Ru. It has now been found that if Ti and Mn in combination are included in a cobalt-containing catalyst, unexpected advantages are obtained.
WO 2014020507; WO 9961550; Applied Catalysis A: General, 419-420 (2012) 148-155; WO 2008104793; WO 2012107718; AU2013203123; US 20120252665 A1; Fuel Processing Technology, 89 (2008) 455-459 and Catalysis Today, 197 (2012) 18-23 disclose the inclusion of Ti in catalysts.
The inclusion of Mn in catalysts is disclosed in Journal of Catalysis, 246 (2007) 91-99; Journal of Physical Chemistry B, 110 (2006), 8626-8639; EP 0966415 A1; U.S. Pat. No. 6,333,294 B1; US 20020010221 A1; Fuel Processing Technology, 90 (2009) 901-908; Journal of Catalysis, 288 (2012) 104-114; Journal of Catalysis, 237 (2006) 152-161; US 20080132589; US 20080064769 A1; US 20100099780 A1 and US 20040127352 A1.
Most surprisingly, it has now been found that when a supported cobalt catalyst includes both titanium and manganese, the activity and/or activity stability of the catalyst and/or the lower methane selectivity of the catalyst and/or the lower support dissolution of the support is improved during hydrocarbon synthesis wherein syngas is contacted with the catalyst. This is shown by the Inventive Examples, for instance in FIGS. 1, 2 and 3 and Table 5, 7, 10 and 12 herein below.